Heart failure (HF) is a debilitating disease in which abnormal function of the heart leads in the direction of inadequate blood flow to fulfill the needs of the tissues and organs of the body. Typically, the heart loses propulsive power because the cardiac muscle loses capacity to stretch and contract. Often, the ventricles do not adequately eject or fill with blood between heartbeats and the valves regulating blood flow become leaky, allowing regurgitation or back-flow of blood. The impairment of arterial circulation deprives vital organs of oxygen and nutrients. Fatigue, weakness and the inability to carry out daily tasks may result. Not all HF patients suffer debilitating symptoms immediately. Some may live actively for years. Yet, with few exceptions, the disease is relentlessly progressive. As HF progresses, it tends to become increasingly difficult to manage. Even the compensatory responses it triggers in the body may themselves eventually complicate the clinical prognosis. For example, when the heart attempts to compensate for reduced cardiac output, it can add muscle causing the ventricles (particularly the left ventricle) to grow in volume in an attempt to pump more blood with each heartbeat. This places a still higher demand on the heart's oxygen supply. If the oxygen supply falls short of the growing demand, as it often does, further injury to the heart may result. The additional muscle mass may also stiffen the heart walls to hamper rather than assist in providing cardiac output, resulting in elevated pressures within the left atrium. Elevated left atrial pressure (LAP) can then exacerbate the HF, particularly congestive HF where the weak pumping of the heart leads to a build-up of fluids in the lungs and other organs and tissues. Often, a progression of HF and the build-up of congestive fluids results in the patient being hospitalized.
Despite current therapies, the rate of HF hospitalizations remains high—about 1.1 million HF hospitalizations annually. A new approach to managing patients has exploited chronic measurements of pulmonary arterial pressures. Pulmonary artery pressure (PAP) is generated by the right ventricle (RV) ejecting blood into the pulmonary circulation, which acts as a resistance to the output from the RV. With each ejection of blood during ventricular systole, pulmonary arterial blood volume increases which stretches the wall of the artery. As the heart relaxes, blood continues to flow from the pulmonary artery into the pulmonary circulation. The smaller arteries and arterioles serve as the chief resistance vessels, and through changes in their diameter, regulate pulmonary vascular resistance. In the recent CHAMPION study, the use of a wireless implantable PAP sensor showed a 30% percent reduction in HF hospitalizations in six months in New York Heart Association (NYHA) Class III HF patients in a prospective, multi-center, randomized (1:1) controlled single blinded clinical trial (n=553). (See, Abraham et al., “Wireless pulmonary artery haemodynamic monitoring in chronic heart failure: a randomised controlled trial,” Lancet 2011; 377:658-666). Use of daily PAP measurements allowed physicians to proactively monitor and tailor the patient's pharmacological therapy. Note that the CHAMPION study was directed to the use of a PAP sensor provided by CardioMEMS, Inc., which operates in conjunction with an external PAP monitor. Briefly, the PAP sensor is implanted within the pulmonary artery of the patient using a catheter. Thereafter, once per day (or at some other periodic interval), the patient places an interface device over his or her chest, which receives PAP data wirelessly from the implanted sensor for routing to a clinician for review.
One technique to address HF is cardiac resynchronization therapy (CRT), which is a pacing technique directed to improving cardiac performance by synchronizing the ventricles. Currently, however, CRT has an estimated 25-30% non-responder rate. Some CRT optimization options are currently available for improving CRT efficacy, such as echocardiography and electrical optimization. However, logistical challenges in echocardiographic optimization make it difficult to incorporate the techniques into common clinical practice and more so for follow-up optimization as cardiac reverse remodeling occurs. In addition, electrical optimization also has its limitations in patients with a marked electromechanical delay. Accordingly, it would be desirable to provide improved CRT optimization techniques. In particular, it would be desirable to exploit beat-by-beat PAP measurements for hemodynamic optimization of CRT therapy as such would provide for real-time assessment of current hemodynamic function within the patient to allow the physician to monitor as well as optimize therapy based on PAP. Hence, some aspects of the present invention are directed to CRT optimization techniques that exploit PAP sensor values.
Mitral regurgitation (MR) is a common finding in patients with left ventricular systolic dysfunction (an aspect of HF) and has been established as an independent predictor of mortality. Indeed, it is estimated that 50% of HF patients have MR, which is a disorder of the heart in which the mitral valve (which separates the left atrium (LA) from the left ventricle (LV)) fails to close properly when the LV pumps blood. The presence of any degree of MR in patients with LV dysfunction is associated with reduced survival. Moreover, the worse the MR, the worse the prognosis. Note that, in patients with MR it has been found that retrograde pressure jets arising due to MR are reflected in the PAP waveform. Accordingly, it would be desirable to provide techniques for exploiting beat-by-beat PAP measurements to detect and track MR and some aspects of the invention are directed to these ends. Such techniques could be exploited within external PAP monitors of the type used in the CHAMPION study or within implantable cardiac rhythm management devices (CRMDs) such as pacemakers, CRTs or implantable cardioverter-defibrillators (ICDs) or within independent non-wireless PAP measurement systems to leverage more frequent or continuous monitoring of pressures as well as data storage/analysis storage.